Security systems are known which are sensitive to the presence of an intruder within a protected space. Different types of sensors are usually employed in a given security installation. Entrances and exits and windows are typically protected by security switches which are activated upon the opening of the associated door or window. Vibration sensors are often employed on glass panes to detect tampering and breakage of the glass. Motion within a protected space is usually sensed by infrared, ultrasonic or electromagnetic motion sensors which provide an output signal in the presence of a detected intruder. The sensors are usually wired or otherwise coupled to a central alarm control which, in turn, is coupled to alarm annunciators and which may be coupled to automatic telephone dialers for calling a predetermined number in the presense of intruder detection.
Mat switches are known for the protection of entrance ways and hallways. These mat switches are, for example, sensitive to the applied pressure of an intruder to cause switch activation and alarm signaling. These mat switches are in the form of a thin mat which typically is installed under a carpet and includes one or more switch contacts activated by a person stepping onto the mat.
A major problem in the design of a security system is to minimize false alarms. Much of the improvement in security systems over the years has been in the improved capability of such systems to discriminate between true intrusion and noise and spurious events which could cause a false alarm.
Present motion sensors are generally operative to detect the presence of a moving intruder, but are not able to track the motion of the intruder within the protected space or to discriminate between intruder size. Thus present motion sensors are triggered by dogs and cats as well as people and cannot be employed if pets are allowed to roam within a protected area. A problem with present mat switches is that furniture placed over the mat can activate the switch contacts, triggering a continuous alarm signal.